Data storage systems are arrangements of hardware and software that typically include multiple storage processors coupled to arrays of non-volatile storage devices, such as magnetic disk drives, electronic flash drives, and/or optical drives, for example. The storage processors service storage requests that arrive from host machines (“hosts”) and that specify files or other data elements to be written, read, created, or deleted, for example. The storage processors run software that manages incoming storage requests and performs various data processing tasks to organize and secure data stored on the non-volatile storage devices.
Data storage systems commonly employ RAID technology to protect the data they store. RAID is an acronym for “Redundant Array of Independent (or sometimes, “Inexpensive”) Disks.” A data storage system may include multiple RAID groups, where each RAID group is formed from one or more disk drives. In some arrangements, a RAID group divides its participating disk drives into segments and forms multiple RAID stripes across corresponding segments on different drives. One or more segments in a RAID stripe may be designated for storing parity information. In the event of a disk failure that damages one of the segments in the RAID stripe, the RAID group can reconstruct the damaged segment using the data and parity information from the remaining segments. It is common practice to arrange segments in RAID stripes so as to promote fast disk access. For example, a RAID group may interleave access to segments on different disk drives to improve overall performance.